JP2018174059A - Welded structure and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a welded portion structure which can suppress the generation of keyholes and has high reliability, and a manufacturing method thereof. SOLUTION: When a battery case 13 and an electrode tab 14 are welded to form a linear welding mark, the laser output is increased to a first output P1 for a first period TP1 from the start of laser irradiation. , After melting the battery case until the electrode tab is melted at the first output, and then maintaining the first output for the second period TP2 to melt the electrode tab and the battery case, After the output of the laser is reduced from the output to the second output P4 that melts only the battery case, the second output is maintained or the output of the laser from the second output is maintained until the formation of welding marks is completed. The amount of decrease is reduced to be smaller than the amount of decrease from the first output to the second output. [Selection diagram] Fig. 2

Description

  The present invention relates to a welded structure and a manufacturing method thereof.

  Sealed secondary batteries such as non-aqueous electrolyte secondary batteries typified by high-capacity lithium ion secondary batteries are widely used as driving power sources for portable devices and the like and storage batteries for home or vehicle use.

  FIG. 8 is a cross-sectional view schematically showing the configuration of the sealed secondary battery. In the sealed secondary battery, an electrode group 4 formed by laminating or winding a positive electrode plate 1 and a negative electrode plate 2 with a separator 3 interposed between them is housed in a battery case 5 together with an electrolyte, and an opening of the battery case 5 is a gasket. A sealing structure sealed with a sealing plate 10 through 6 is formed. The positive electrode tab 11 introduced from one electrode plate (for example, positive electrode plate) of the electrode group 4 is joined to the sealing plate 10 also serving as one external terminal, and is led out from the other negative electrode plate of the electrode group 4. The negative electrode tab (not shown in FIG. 8) is joined to the battery case 5 which also serves as the other external terminal.

  As a method of irradiating a laser case to a conventional battery case made of a metal such as iron or SUS and a negative electrode tab made of nickel or copper, a laser is irradiated from the outside of the battery case 5. Some are welded (see, for example, Patent Document 1). 9 and 10 are views showing welding of the battery case bottom 13 of the conventional battery case 5 described in Patent Document 1 and the negative electrode tab 14.

  In FIG. 9, an electrode group 4 formed by winding a positive electrode plate and a negative electrode plate in a spiral shape through a separator is inserted into a cylindrical battery case 5, and the negative electrode tab 14 welded to the negative electrode plate is connected to the battery case 5. The battery case 5 is overlapped with the bottom 13 of the battery case 5 at the center of the battery case, the negative electrode tab 14 is brought into contact with the bottom 13 of the battery case 5 with the contact rod 12, and the pulse laser 7 is irradiated from the outside of the battery case 5. The battery case bottom 13 and a part of the negative electrode tab 14 are welded.

  In the configuration disclosed in Patent Document 1, the pulse laser 7 is irradiated from the outside of the battery case 5, and while the temperature of the tab surface is measured, a plurality of pulse irradiations are continued until the signal exceeds a certain threshold value. .

  By the way, although the method of irradiating the pulse laser 7 from the negative electrode tab 14 side inside the battery case 5 is also conceivable, there is a possibility that the pulse laser 7 hits the electrode group 4 and burns, and spatter generated during welding If by-products such as debris remain inside the battery case 5, it may cause a short circuit failure. Therefore, the method of irradiating the pulse laser 7 from the outside of the battery case 5 described in Patent Document 1 is desirable. .

  FIG. 10 is a cross-sectional view showing a joint between the battery case bottom 13 and the negative electrode tab 14 of the battery case 5 of FIG. 9, and the surface of the battery case bottom 13 is irradiated by irradiating the pulse laser 7 from the battery case bottom 13 side. As the irradiation progresses, the welded portion 15 having the linear weld trace reaches the joint surface with the negative electrode tab 14 and further stops inside the negative electrode tab 14 to stop laser irradiation, and the battery case 5 case bottom part 13 and negative electrode tab 14 are joined. In general, in the welding by the pulse laser, since a plurality of irradiations are continued at the same place, the heat of the laser is concentrated at one point, and this heat is transferred into the material by heat conduction, and welding on the pulse laser 7 irradiation side of the battery case bottom 13 is performed. The welding area of the part 15 becomes large.

  In addition, as a method of welding a conventional sealing plate made of a metal such as aluminum and a positive electrode tab made of aluminum by irradiating a laser, the other end of the tab is brought into contact with the sealing plate, and the thickness of the tab In some cases, the other end of the tab is laser welded to the sealing plate by irradiating from the tab side while continuously scanning a fiber laser beam having a spot diameter smaller than that (for example, see Patent Document 2).

  In the configuration disclosed in Patent Document 2, deep penetration welding (keyhole welding) is performed with a smaller spot diameter using a fiber laser.

  The keyhole welding will be described in detail with reference to FIG. When the laser output density is high, the surface of the laser irradiation part is heated to the evaporation temperature or higher, the surface is recessed by the reaction force during evaporation, and a deep keyhole is formed. In the keyhole, the laser is Fresnel absorbed (absorbed by multiple reflection) at the inner wall surface of the keyhole (generally, the front wall surface in the traveling direction) or at the bottom, and metal vapor (plume) is generated and ejected from the keyhole port. The penetration depth of the keyhole fusion weld is determined by the keyhole depth and the hot water flow from the tip. Here, the portion where the hot water flow is convection while the laser beam is traveling is referred to as a molten pool. In this molten pool, heat is diffused by heat conduction to surrounding materials and heat convection to the atmosphere, and gradually cools and hardens.

12 and 13 are diagrams showing welding of the sealing plate 10 and the positive electrode tab 11 in the related art described in Patent Document 2. FIG. FIG. 12 is a plan view showing a method of laser welding the conventional positive electrode tab 11 described in Patent Document 2 to the sealing plate 10. FIG. 13 is a view showing a cross section of a welded portion composed of the positive electrode tab 11 and the sealing plate 10.
In FIG. 13, a continuous wave laser 16 having a spot diameter smaller than the thickness of the positive electrode tab 11 in a state in which the end portion of the positive electrode tab 11 led out from the electrode group is in contact with the sealing plate 10 is connected to the positive electrode tab 11. The welded portion 15 is formed by continuously scanning along the width direction 11, and the end portion of the positive electrode tab 11 is laser welded to the sealing plate 10.

JP 2004-158318 A Patent No. 4647707

However, the above structure has a problem that a keyhole is generated.
An object of the present disclosure is to provide a welded structure and a manufacturing method thereof that can suppress the possibility of occurrence of a keyhole and have high reliability.

In order to solve the above problems, a method for manufacturing a welded structure according to the present disclosure includes a welded structure welded by scanning a laser from the outer surface of the battery case in a state where the inner surface of the battery case is in close contact with the electrode tab. A manufacturing method of
Forming a linear welding mark by relative movement between the laser and the battery case;
In the process,
During the first period after the start of the laser irradiation, the laser output is increased to the first output, the battery case is melted until the electrode tab is melted at the first output, and then
During the second period, maintaining the first output, melting the electrode tab and the battery case, then
Decreasing the output of the laser from the first output to a second output that melts only the battery case, then
When the second output is maintained until the end of the formation of the weld mark, or the amount of decrease in the laser output from the second output is reduced from the first output to the second output Less than the amount of decrease.

  As described above, according to the present disclosure, after the electrode tab and the battery case are melted, the laser output is reduced until reaching the second output for melting only the battery case, and then the welding is performed. The second output is maintained until the end of the formation of the mark, or a decrease when the amount of decrease in the laser output from the second output is reduced from the first output to the second output. It is smaller than the amount. As a result, the amount of melting at the laser end portion is increased, and even if a keyhole is generated due to, for example, a resin-based foreign matter present at the interface between the battery case and the electrode tab, It is possible to suppress the generation of keyholes by filling the holes.

The figure explaining the laser output control with respect to the elapsed time of this Embodiment 1. The figure explaining the welding part cross section of this Embodiment 1. The figure explaining the laser output control with respect to the elapsed time of this Embodiment 1. The figure which shows the cross-sectional area of the down slope part formed by the manufacturing method of the welded structure of this Embodiment 1. A diagram explaining the generation of through holes when there is a new joint between the bottom of the battery case and the negative electrode tab formed in the down slope due to variations in laser output The figure explaining the laser output control with respect to the elapsed time of this Embodiment 2, and a laser scanning speed. The figure explaining the welding part upper surface and cross section of this Embodiment 2. Sectional view schematically showing the configuration of the sealed secondary battery The figure which shows the welding method of the conventional battery case and negative electrode tab which were described in patent document 1 The figure which expanded the cross section of the welding part of the conventional battery case and negative electrode tab which were described in patent document 1 Illustration explaining keyhole welding The figure which shows the welding method of the conventional sealing board described in patent document 2, and a positive electrode tab The figure which expanded the cross section of the welding part of the conventional sealing board described in patent document 2, and a positive electrode tab The figure explaining the welding when the resin-type foreign material pinched | interposed between the case bottom and the negative electrode tab exists in the approximate center of a welding area. CT image of the blowhole remaining inside the melt The figure explaining the welding when the resin-type foreign material pinched | interposed between the case bottom part and the negative electrode tab exists in a laser irradiation termination part. CT image of a through-hole generated at the end of laser irradiation The through hole is observed from the bottom side of the battery case Top view and sectional view of case bottom and negative electrode tab welded with joint length S1 The figure explaining the laser output control with respect to the elapsed time of FIG. Top view and cross-sectional view of battery case bottom and negative electrode tab welded with joint length S2 The figure explaining the laser output control with respect to the elapsed time of FIG. The figure explaining the output control with respect to the elapsed time at the time of making a laser scanning speed 2 times the conventional.

  Hereinafter, the present embodiment will be described with reference to the drawings. In the following graphs, when the horizontal axis is a time graph, the start time of the output change command is the time on the left side of the bar graph.

First, the knowledge that has led to this embodiment will be described.
Resin-based foreign matter such as PET or oil adhered to the surface of the battery case bottom 13 or the negative electrode tab 14 that has occurred in the manufacturing process or adhered in the previous process is on the inner wall surface or bottom of the keyhole during welding. When the multiple reflected laser is touched, the resin foreign matter or oil rapidly sublimates, expands in volume, and generates gas. This gas is ejected from the keyhole port, and at this time, the hot water flow around the keyhole is also blown off and sputtered to generate a hole larger than a normal keyhole. In keyhole welding, welding proceeds while filling the generated keyhole with the flow of hot water from the front with respect to the welding direction. If the amount of hot water flow is large, the generated hole can be filled.

  However, iron or SUS used for the battery case 5 has a thermal conductivity as small as about 1/4 and a melting point as large as about 2.5 times that of aluminum to be welded described in Patent Document 2, Little hot water flow is generated.

  In particular, since the laser irradiation terminal portion gradually weakens the laser beam, the amount of hot water flow generated in the scanning forward direction gradually decreases, and it becomes difficult to fill the generated holes.

  In addition, since the amount of hot water flowing at the time of laser irradiation is reduced, resin foreign matter such as resin or oil interposed between the battery case bottom 13 and the negative electrode tab 14 as described in Patent Document 2 As a result, there is a problem in that a hole is easily opened in the can during laser welding. If a hole is opened in the can, leakage of the electrolyte will occur.

  A specific process of generating a through hole at the bottom of the battery case will be described with reference to FIGS. 14 and 16 are cross-sectional views, but hatching is omitted because hatching makes it difficult to understand.

  FIG. 14 shows keyhole welding between the battery case bottom 13 and the negative electrode tab 14 when the resin-based foreign material 17 sandwiched between the battery case bottom 13 and the negative electrode tab 14 is at the center of the scanning range of the laser 16. It is a figure explaining the process state joined by this. 14A is a cross-sectional view and a top view of the process state at a position immediately before the resin-based foreign material 17 when the laser 16 is moved. FIG. 14B is a cross-sectional view and a top view of the process state at the position on the foreign material 17. FIG. 14 (3) is a cross-sectional view and a top view of the process state at a position immediately after the foreign material 17. Description will be made with reference to these drawings.

  First, in FIG. 14 (1), at a position immediately before the resin-based foreign material 17, a hot water flow 21 is generated behind the generated keyhole 19 in the laser welding direction, and the keyhole generated in the past in time. 20 is filled with the hot water flow 21 flowing from the front in the welding direction to the keyhole 20 and disappears, and gradually cools to form the solidified portion 23. This is the normal keyhole welding process state.

  Next, in (2) of FIG. 14, when the laser 16 comes to a position on the foreign matter of the resinous foreign matter 17 and comes into contact with the resinous foreign matter 17, the resinous foreign matter 17 in contact with the laser 16 rapidly sublimates, Due to the upward pressure 25 due to the sublimation, an enlarged keyhole 27 in which the inner diameter of the keyhole 19 is enlarged is generated. The inner diameter of the enlarged keyhole 27 is larger than the inner diameter of the keyhole 19 generated at a position immediately before the resin-based foreign material 17 (see (1) in FIG. 14).

  However, at this time, since the amount of the hot water flow 21 flowing from the front is large, as shown in FIG. 14 (3) at the position immediately after passing through the resin foreign matter 17, the generated enlarged keyhole 27 is The molten pool 22 is filled with the hot water flow 21 flowing from the front. However, when the size of the resin foreign matter 17 is large and the generated enlarged keyhole 27 cannot be completely filled with the molten metal flow 21, or when the welding speed is high, the molten metal flow 21 flowing from the front decreases. In some cases, the blow hole 26 may remain inside the molten pool 22 as shown in the figure immediately after the laser 16 passes through the resin foreign material 17 and is not filled with the hot water flow 21 (3). Note that reference numeral 19a in (3) of FIG. 7 is a keyhole generated immediately after (3) when the laser 16 passes through the resin foreign matter 17.

  FIG. 15 is a CT (Computed Tomography) image of the blow hole 26 remaining inside the molten pool 22, and this blow hole 26 is usually present at the boundary between the battery case bottom 13 and the negative electrode tab 14. ing.

  Next, when the resin-based foreign material 17 sandwiched between the battery case bottom 13 and the negative electrode tab 14 is at the irradiation end portion of the laser 16, the battery case bottom 13 and the negative electrode tab 14 are joined by keyhole welding. The process state will be described with reference to FIG. FIG. 16A is a cross-sectional view and a top view of the process state at a position immediately before the resin-based foreign material 17 when the laser 16 is moved. FIG. 16B is a cross-sectional view and a top view of the process state at the position on the foreign material 17. FIG. 16 (3) is a cross-sectional view and a top view of the process state at a position immediately after the foreign material 17. Description will be made with reference to these drawings.

  First, in (1) of FIG. 16, in the state immediately before the resin-based foreign matter 17, the generated keyhole 19 is moved from the front in the welding direction to the keyhole 19 in the same manner as described in (1) of FIG. It is filled with the flowing hot water flow 21 and disappears.

  Next, in FIG. 16 (2), when the laser 16 comes to the position of the resin-based foreign material 17 on the foreign material and comes into contact with the resin-based foreign material 17, as in the description of (2) of FIG. An enlarged keyhole 27 having an inner diameter larger than the inner diameter of the keyhole 19 generated at the position immediately before (1) of the resin foreign matter 17 is generated.

  However, in contrast to the description in FIG. 14, in FIG. 16, the generation part of the enlarged keyhole 27 is at the end of irradiation of the laser 16, and the output of the laser 16 gradually decreases. For this reason, since the hot water flow 21 flowing from the front in the welding direction is small as compared with the explanation in FIG. 14 (3), the enlarged keyhole 27 generated by the hot water flow 21 is filled. It is highly possible that this is not possible, and the through hole 28 remains.

  FIG. 17 is a CT image of the through hole 28 generated at the laser irradiation terminal portion. The through hole 28 exists across the battery case bottom 13 and the negative electrode tab 14.

  FIG. 18 is an SEM photograph of the through hole 28 observed from the battery case bottom 13 side. On the rear side of the generated through hole 28 in the welding direction, a melt swell 24 is formed by the upward pressure 25 when the resin-based foreign material 17 sublimates.

  From the above description, in the keyhole welding with the laser 16 having a beam diameter sufficiently smaller than the thickness of the battery case bottom 13 from the battery case bottom 13 side to the battery case bottom 13 and the negative electrode tab 14, the irradiation termination portion of the laser 16 Therefore, the probability that the through hole 28 is generated is high. The reason is that, at the irradiation end portion of the laser 16, since the amount of the hot water flow 21 flowing from the front in the welding direction is small, the generated enlarged keyhole 27 cannot be filled with the hot water flow 21, and the through hole 28 is formed. The probability of remaining increases.

  On the other hand, the area of the joint between the battery case bottom 13 and the negative electrode tab 14 is a parameter that determines the joint strength between the battery case bottom 13 and the negative electrode tab 14. In addition, a certain area or more of the joint portion is required.

  A method for setting welding conditions for ensuring a certain level of bonding strength between the battery case bottom 13 and the negative electrode tab 14 will be described with reference to FIGS.

19 (a) and 19 (b) are top views as seen from the battery case bottom 13 side when welding is performed at the length S1 in the scanning direction of the laser 16 of the joint 31 between the battery case bottom 13 and the negative electrode tab 14. FIG. A sectional view is shown. When the battery case bottom 13 and the negative electrode tab 14 are joined, the depth h1 of the welded portion 15 that is a linear weld mark is always in a relationship of h1> B with respect to the thickness B of the battery case bottom 13. . In (a) and (b) of FIG. 19, welding starts from the left side, and welding proceeds toward the right side. Scanning speed of the laser 16 at this time is a constant velocity V _1. Further, in the top view of FIG. 19A, if the length of the appearance of the welded portion 15 is L and the width is W, the length L is determined by the scanning distance of the laser 16, and the width W is the laser. 16 is determined by the beam diameter of 16 and the scanning speed of the laser 16. That is, when the scanning speed V ₁ of the laser 16 is low, the width W is usually larger than the beam diameter of the laser 16 due to melting of the metal due to heat conduction to the surroundings.

  In the welding start portion of the laser 16, that is, in the section of the joint length S0, in order to suppress the generation of spatter, the laser output is gradually increased gradually to increase the penetration depth. This is also a method described in Patent Document 2 and is for preventing spatter from scattering to the surroundings. If energy is suddenly injected into the metal, the solid-> melt-> fluid phase transformation becomes unstable and a lot of spatter is generated. The depth of the welded portion 15 at the joint is maintained at h1. On the other hand, in the welding end portion of the laser 16, that is, in the section having the length S2 of the joint portion, the laser output is gradually and gradually reduced to reduce the penetration depth so as to fill the keyhole generated during welding. The length in the scanning direction of the laser 16 of the cross section of the welded portion where the laser output is gradually reduced continuously at the end of the weld is defined as S2.

  FIG. 20 is a diagram for explaining the laser output control with respect to the elapsed time from the start of welding when forming the welded portion 15 in FIG. 19. The horizontal axis represents the time since the laser oscillation, and the vertical axis represents the laser output at the processing point at each time.

  The time resolution of the laser output control is about 0.1 ms at the minimum although it depends on the device that controls the laser oscillator. A white square 32 in FIG. 20 is a laser output setting value of a processing point at each elapsed time.

The laser output is gradually increased from the start of welding, and the case bottom 13 and the negative electrode tab 14 are joined at an output P1 or higher. In addition, since the laser 16 penetrates the negative electrode tab 14 above the output P2, the output is set between P1 and P2. At the time t ₀ , the output is equal to or higher than the output P _{1 and} is maintained only for the time Δt ₁ to secure the length S 1 of the joint. Laser In the welding terminal end, gradually lowering the laser output continuously and gradually gradually at time t _1, the time Δt laser output at time t ₂ after ₂ elapses welding zero completed.

Next, a method for setting welding conditions for increasing the welding strength between the battery case bottom 13 and the negative electrode tab 14 at the scanning speed V ₁ of the laser 16 without changing the welding appearance length L on the battery case bottom 13 side. This will be described with reference to FIGS. 21 and 22.

Similarly, from the start of welding, the laser output is gradually increased gradually, and the case bottom 13 and the negative electrode tab 14 are joined at an output P1 or higher. A time t ₀ from when the laser output is increased until it becomes equal to or higher than the output P1 is a necessary time for suppressing the generated sputtering. A constant value equal to or higher than the output P1 is maintained only for the time Δt ₃ (= second period TP2), and the length S3 (> S1) of the joint portion is ensured. Laser welding end section, will gradually lowered laser output at time t _3, the laser output becomes zero at time t ₄ of time Delta] t ₃ after the welding is completed. However, the length S4 of the cross section of the welded portion in which the laser output is continuously reduced gradually at the welding end portion is shorter than the length S2. For this reason, when the enlarged keyhole 27 is generated by the resinous foreign material 17 at the irradiation end portion of the laser 16, the amount of the hot water flow 21 for filling the enlarged keyhole 27 is reduced, and the through hole 28 may be generated. Is even higher.

Further, when the scanning speed V ₁ of the laser 16 is set to a double speed V ₂ , the time resolution of laser output control is not changed to 0.1 ms. Therefore, as shown in FIG. When the enlarged keyhole 27 is generated by the resinous foreign matter 17 at the irradiation end portion of the laser 16, the area of the cross section of the welded portion that becomes coarser and the laser output is gradually reduced gradually becomes smaller. The amount of the hot water flow 21 for filling 27 is reduced, and the possibility that the through hole 28 is generated is further increased.

  The present disclosure solves the above-described conventional problems. When the enlarged keyhole 27 is generated by the resin-based foreign matter at the irradiation end portion of the laser 16, the amount of hot water flow for filling the enlarged keyhole 27 is increased. Therefore, it is an object of the present invention to provide a welded part structure such as a battery and a manufacturing method thereof to suppress the possibility of the occurrence of a through-hole 28 that can be formed at the irradiation terminal part of the laser 16 due to the presence of a resinous foreign matter.

(Embodiment 1)
FIG. 2 shows a cross-sectional structure of a welded portion between a battery case bottom 13 and a negative electrode tab 14 of a cylindrical battery as an example of the welded structure in the first embodiment. In this battery, the battery case bottom 13 and the negative electrode tab 14 are joined by a welded portion 15 </ b> A so that the inner surface of the battery case bottom 13 is in close contact with the negative electrode tab (an example of an electrode tab) 14. The welded portion 15 </ b> A is continuously formed so as to reach from the outer surface of the battery case bottom 13 to the inside of the negative electrode tab 14. Moreover, FIG. 1 shows the elapsed time from the start of welding in order to realize the cross-sectional structure of the welded portion 15A of the linear weld trace between the battery case bottom 13 and the negative electrode tab 14 of the cylindrical battery in the first embodiment. It is a figure explaining laser output control. In FIG. 1, when the time resolution of the laser output control is 0.1 ms, the white square 32 is an integrated value of the laser output at the processing point at each time. The black line 33 is a line connecting the average values of the laser outputs at each time. In the figure, the time t ₀ etc. is set as the start time of the laser output change command (the left end of the rectangle 32), and the period TP1 etc. and the time Δt ₃ etc. are based on the average value of the laser output (black line 33). This will be described below.

  In FIG. 2, the material of the battery case bottom 13 is made of, for example, iron or SUS. As an example, when the battery case bottom 13 is made of iron, the surface is coated with nickel having a thickness of several microns to prevent corrosion. The negative electrode tab 14 has, for example, simple nickel or a laminated structure of nickel layer / copper layer / nickel layer.

  At the time of laser welding, from the negative electrode tab 14 side, the negative electrode tab 14 is pressed against the battery case bottom 13 by a heat-resistant rod-shaped jig, and from the laser irradiation direction side, a portion other than the laser irradiated portion is pressed by a jig or the like. As a result, the battery case bottom 13 and the negative electrode tab 14 are laser-welded in close contact with each other.

In a laser welding method, which is an example of a method for manufacturing a welded structure, a linear welding mark is formed by relative movement between the laser and the bottom 13 of the battery case.
Specifically, this laser welding method includes at least the following four steps.
(A), during a first period TP1 from after the start laser irradiation to the time t _0, by increasing the output of the laser to the first output P1, the first output P1, up to the melting of the electrode tabs 14 The battery case bottom 13 is melted.
(B) Thereafter, that is, after the first period TP1, during the second period TP2, the first output P1 is maintained, and the electrode tab 14 and the battery case bottom 13 are melted.
(C) After that, that is, after the second period TP2, the laser output is decreased from the first output P1 to the second output P4 that melts only the battery case bottom 13.
(D) Thereafter, the second output P4 is maintained until the end of the formation of the weld mark (see Embodiment 2 described later), or the amount of decrease in the laser output from the second output P4 is set to the first output P1. To a second output P4, the amount of decrease is smaller.

Process of the (c) and (d) is performed during the third period TP3 for a period of time Delta] t _4, until the end formation of the welding mark, it does not reduce the output of the laser to zero.

More specifically, the process is performed as follows.
When the laser 16 is scanned at a constant speed V ₁ by a scanner such as a galvanometer mirror with respect to the battery, or when the laser is scanned at a constant speed by moving a stage or the like holding the battery case, FIG. , only the first period TP1 from the start laser irradiation to the time t _0, continuously and gradually increased until the laser output (an example of the first output) P1 for bonding the laser output and the battery case bottom 13 a negative electrode tab 14 Thus, at the first output P1, the battery case bottom 13 is melted until the negative electrode tab 14 is melted. The first output P1 is an output for melting the negative electrode tab 14 and melting the battery case bottom 13.

Here, in FIG. 2, the penetration depth at the laser output P1 is h1. The first period TP1 and the first section distance S0 from the laser irradiation start up time t _0, in the present embodiment 1 is referred to as up-slope. The laser output P0 is a critical output at which the battery case bottom 13 and the negative electrode tab 14 are welded. The laser output P2 is an output through which the laser 16 penetrates the negative electrode tab 14. The laser outputs P0, P1, and P2 Is always P0 <P1 <P2.

For example, the battery case bottom 13 is made of SUS with a thickness of 0.3 mm with Ni plating having a thickness of several μm, and the negative electrode tab 14 has a laminated structure of nickel layer / copper layer / nickel layer = 25 μm / 50 μm / 25 μm. Then, normally, the time t ₀ is required for the first period TP1 = 0.5 ms, and when the constant speed is V ₁ = 200 mm / s, the first section distance S0 = 0.1 mm. As an example, when the laser output P1 (first output) is 800 to 850 W, the penetration depth is h1 = 0.34 to 0.35 mm. Here, the first output P1 is an output that welds the battery case bottom 13 and the negative electrode tab 14 and is not less than half the thickness of the negative electrode tab 14 and does not penetrate the tab thickness, and is set to 800 to 850 W as an example. it can.

In FIG. 1, since the laser output control has a time resolution of 0.1 ms, the laser output gradually increases. The first period TP1, i.e., when the time _{t 0} is too short, for example, with respect to SUS thickness 0.3mm to Ni plating of the number μm thickness is applied, about 0.2ms following upslope time t _{At 0} , the laser irradiated SUS suddenly increases in temperature and enters a molten state, and a large amount of spatter is generated due to the reaction force due to the rapid temperature increase.

When a lot of spatter occurs, the optical component for condensing the laser 16 becomes dirty, the laser is shielded from light due to the dirt, the output of the laser is weakened, welding failure occurs, spatter enters the battery case, When a battery is used, a short circuit failure may be caused, or a secondary failure may occur. Therefore, in order to suppress spatter scattering to the periphery, it is desirable to secure the upslope time t _0, that is, the first period TP1 for 0.5 ms or more and continuously increase the laser output.

Next, in FIG. 1, after the laser output reaches the first output P1, the laser output is kept constant at the first output P1 for the second period TP2 = Δt ₃ hours, and the negative electrode tab 14 and the battery case The bottom 13 is melted. The welding length at this time is S3, and the longer the welding length S3, the stronger the bonding strength between the battery case bottom 13 and the negative electrode tab 14.

For example, the torque strength of a battery case bottom 13 and the negative electrode tab 14, the bonding length and S3 S3 = 2 mm in the case 10 N · m required above, the constant velocity _{V 1} and _V 1 = 200mm / s, the second The period TP2 = Δt ₃ = 10 ms.

Next, in FIG. 1, after the time _{t 3} from the start of laser irradiation (i.e., the first period TP1 and the second period TP2 after) during the time Delta] t ₄ as a third period TP3 of the laser output from the laser output P1 Decrease. Wherein the laser output P1, lowering the laser output gradually, laser output laser output (second output of the example) through P4 time to time t ₄ when made in the laser output P5 Delta] t 4 ₌ the third period TP3 third section The distance S4 is referred to as a down slope portion DS in the first embodiment. In the conventional welding method described in Patent Document 2, the laser output is simply continuously reduced. In contrast, in the present embodiment 1, in the middle between the third period TP3 = Time Delta] t ₄ after time t ₃ of the laser output P1, the laser output from the laser output P1, the battery case bottom 13 The laser output is gradually lowered to a laser output (an example of a second output) P4 that is 50 to 97% of the laser output P0, which is a critical output to which the negative electrode tab 14 is welded. Thereafter, during the remaining time Δt ₄ , the laser output P4 is gradually decreased from the laser output P4, and the laser output P5 below the laser output P4 is maintained until the end of the laser irradiation unit. The laser output P5 is 20 to 50% of the laser output P0 in order to achieve a desired effect. Accordingly, during the third period TP3 = Time Delta] t _4, the laser output is the laser output P5 from the laser output P1 (an example of the second output) laser output through P4. The second output P4 is an output for melting only the battery case bottom 13. In other words, when the variation of the laser output is about ± 3%, at the end of the formation of the weld trace, at least 0.97 of the laser output P0 which is a critical output at which the battery case bottom 13 and the negative electrode tab 14 are welded. It is sufficient that double laser output remains.

In addition, as the minimum time of the time Δt ₄ ,
h _5min = DS2-V ₂₈ = B / 2S4 × (π × W−2S4)
From this formula:
S4 = πWB / 2 / (h _5min + B).
Here, when the laser scanning speed was set to V _1,
Δt ₄ — _min = S4 / V ₁ is _satisfied .

As an actual value, when π = 3.141592654, W = 0.05 mm, B = 0.3 mm, h 5 _—min = 0.2 mm, S4 = 0.047212389 mm, V ₁ = 200 mm / s, Δt 4 _—min = 0 .000235619s = 0.235619449 ms.
Therefore, the minimum time of the time Δt ₄ is 0.2 ms, and the third period TP3 = Δt ₄ = 0.2 ms. The welding appearance length L is L = S0 + S3 + S4 = 0.1 mm + 2 mm + 0.04 mm = 2.14 mm.

  Under this condition, an inflection point 34 that does not exist in the prior art of FIG. 21 is formed in the cross section of the down slope portion DS in FIG.

  Here, the larger the cross-sectional area of the down slope portion DS, the larger the amount of the hot water flow 21 (in other words, the amount of the molten pool) that fills the through hole 28 described in FIGS. 16 to 18, and the depth h4 = h5. That is, when the laser output is 50% of P4 = P5 = P0, the filling effect of the through hole 28 is maximized. That is, in accordance with the laser output control profile shown in FIG. 3, after scanning the laser until the output becomes laser output 0 → P0 → P1 → P4, the laser output P5 of the laser output P4 or less is continued until the end of the laser irradiation unit. Maintain and process. Thereby, as shown in FIG. 4, the down slope part DS with a higher filling effect of the through hole 28 can be formed.

  In addition, h4 is the depth of the inflection point 34, and h5 shows the penetration depth at the end point of the welded portion 15A. A region formed up to the laser output P4 (inflection point 34) is referred to as a first down slope portion DS1, and a region from the inflection point 34 to the end point of the welded portion 15A is referred to as a second down slope portion DS2. Sometimes called. That is, the welded portion 15A has a first down slope portion DS1 and a second down slope located on the outer side of the first down slope portion DS1 in the side region of the welded portion 15A in the cross section in the thickness direction of the negative electrode tab 14. And a slope portion DS2. The first down slope portion DS1 exists over both regions of the negative electrode tab 14 and the battery case bottom portion 13, and its thickness gradually decreases toward the outside. The second down slope portion DS2 exists only in the region in the battery case bottom portion 13, and the thickness change amount thereof is smaller than that of the first down slope portion DS1.

Finally, in FIG. 1, after the time from the start laser irradiation _{t 4} (i.e., the first period TP1, the second period TP2, and the third period TP3 after), the stop laser output, the present embodiment 1 Welding of battery case bottom 13 and negative electrode tab 14 is completed.

  Here, the thickness of the second down slope portion, in other words, the fusion depth h4 is 97% at the maximum with respect to the thickness B of the battery case bottom portion 13 (second output P4 = 770 to 820 W). For example, when B = 0.3 mm, the maximum depth of the inflection point 34 is desirably h4 = 0.29 mm, and when the penetration depth h4 is small (less than 50% of the thickness B), The amount of the hot water flow 21 for filling the through hole 28 opened in the bottom 13 of the battery case is small, and the hole filling effect is small. In addition, when the penetration depth h4 is too close to the thickness B of the battery case bottom 13 (more than 97% of the thickness B), the downslope portion may vary due to material thickness variation or laser output variation. In section S4, the battery case bottom 13 is penetrated, and there is a high possibility that a new hole will be generated by contacting another resin foreign substance or the like interposed between the battery case bottom 13 and the negative electrode tab 14 between the down slope portions. . FIG. 5 is a diagram for explaining the generation of the through hole 28 when there is a new joint portion 35 between the battery case bottom portion 13 and the negative electrode tab 14 formed in the down slope portion due to variations in laser output. In order not to leave such a new joint 35 and through hole 28, the inflection point 34 is arranged in the battery case bottom 13 and the thickness of the second down slope portion DS2, in other words, the inflection point. The distance from the surface of 34 is 50% or more of the thickness B of the battery case bottom 13 and 97% or less of the thickness B. Here, the second output P4 is an output of −3% to −5% of an output that can penetrate the battery case bottom portion 13, and can be set to 770 to 820 W as an example.

  As described above, according to the first embodiment, the laser output is decreased from the first output P1 to the second output P4 in which only the battery case bottom 13 is melted at the irradiation terminal portion of the laser 16, and then the second output. The amount of decrease in the laser output from P4 is made smaller than the amount of decrease when decreasing from the first output P1 to the second output P4. As a result, the amount of melting at the end of the laser (amount of hot water flow) is increased, and even if a resin-based foreign matter is present at the interface between the battery case bottom 13 and the negative electrode tab 14 and a through hole is generated, a large amount of melting occurs. It is possible to fill the through holes with the amount and suppress the generation of holes. Therefore, for example, when the enlarged keyhole 27 is generated by the resin-based foreign matter at the irradiation end portion of the laser 16, the enlarged keyhole 27 can be sufficiently filled with a large melting amount. As a result, even if a resin-based foreign matter is present at the interface between the battery case bottom 13 and the negative electrode tab 14, the generation of the through hole 28 can be suppressed, and a highly reliable welded part structure and a manufacturing method thereof are provided. can do.

(Embodiment 2)
The second embodiment is a method for further increasing the amount of molten pool (the amount of hot water flow) in the down slope portion DS than in the first embodiment.

  FIGS. 7A and 7B are a top view and welding of the battery case bottom 13 and the negative electrode tab 14 of the cylindrical battery according to Embodiment 2 of the present invention viewed from the battery case bottom 13 side (outer surface side). It is a cross-sectional side view which shows the cross-section of a part. FIG. 6 is a welding method for realizing a welded cross-sectional structure of the battery case bottom 13 and the negative electrode tab 14 of the cylindrical battery according to Embodiment 2 of the present invention, and FIG. The time is represented, and the set value of the laser output is represented on the vertical axis. The laser output setting resolution is 0.1 ms.

In FIG. 7, as in the first embodiment, when the laser 16 is scanned at a constant speed V ₁ by a scanner such as a galvanometer mirror, or when the stage holding the battery case is moved, the constant speed V _{1 is used.} in when the laser 16 is scanned cell, only the first period TP1 from the start laser irradiation to the time t _0, by increasing the output of the laser continuously, at a first output P1, to melt the negative electrode tab 14 The battery case bottom 13 is melted until it reaches.

Next, after the laser output reaches the junction output between the battery case bottom 13 and the negative electrode tab 14, that is, the first output P1, the time Δt ₃ from time t ₀ to time t ₃ (ie, the second output) During the period TP2), the laser output is maintained at the constant first output P1, and the negative electrode tab 14 and the battery case bottom 13 are melted.

Then, after the (i.e., the first period TP1 and the second period TP2 after) the time _{t 3} between Delta] t ₄ (i.e., during the third period TP3), the laser output, laser output from the laser output P1 together reduced to P6, the scanning speed of the laser also reduces the scanning speed V ₁ to the scanning speed V _4. By slowing down the scanning speed, the amount of hot water flow can be increased by heat conduction to the surroundings. Here, the laser output P6 is P1>P0>P6> 0, P6 _max = P0 × 0.97 (because the laser output variation is ± 3%), and P6 _min = P5 _min . Further, the scanning speed V ₄ is V ₁ > V ₄ > 0. By combining the laser output and the laser scanning speed, as shown in a plan view of the welded portion in FIG. 7, the laser irradiation portion end 15B is thicker than the normal appearance width W (the center portion of the welded portion 15A), and the width W3 is set. It is possible to increase the amount of hot water flow in the down slope portion, and the effect of filling the generated through hole 28 is increased. The portion corresponding to the second down slope portion DS2 excluding the curved end edge portion of the laser irradiation portion end 15B has a constant width W3 regardless of the location.

Appearance width of the laser irradiation portion terminating 15B W3, in other words, the outer surface of the battery case bottom 13, weld appearance width W3 corresponding to the down slope part DS is laser output P6, the scanning speed V _4, and the proportionality constant k6 Can be expressed by the following equation.
W3 = k6 × P6 / V ₄
The proportionality constant k6 is a constant that depends on the thermal conductivity of the material.

On the other hand, the penetration depth h6 of the down slope portion DS can be similarly expressed by the following equation.
h6 = S6 × P6 / V ₄
The proportionality constant S6 is a constant that depends on the thermal conductivity of the material.

Now, as a condition for increasing the amount of hot water flow in the down slope portion DS of Embodiment 1, when the thickness of the battery case bottom 13 is B,
0.5 × B ≦ h6 ≦ 0.97 × B
0.5 × B ≦ (S6 / k6) W3 ≦ 0.97 × B
It becomes.

Furthermore, as a condition for increasing the amount of hot water flow in the down slope portion DS than in the first embodiment,
W3> W
It becomes.
The welding appearance width W3 of the downslope portion DS in the second embodiment is a width that satisfies the above formula.

  In addition, since the scanning speed of only the down slope portion DS is reduced, the productivity is not greatly reduced.

For example, when the laser scanning speed V ₁ = 200 mm / s, when the joint output P1 = 850 W, the welding width W = 0.15 mm, and the welding width of the down slope portion DS is desired to be nearly double W3 = 0.2 mm. When the laser scanning speed is half V ₄ = 100 mm / s and the laser output is also half P6 = 400 W, a welding width W3 = 0.2 mm is obtained. The fusion depth at this time is h6 = 0.15 mm.

When welding appearance length L = 2.14 mm, S0 = 0.1 mm, S3 = 2 mm, S4 = 0.04 mm, welding time is TP1 + TP2 + TP3 = 0.1 msec + 10 msec
+0.08 msec = 10.9 msec, TP1 = 0.5 msec, TP2 = 10 msec, TP3 = 0.2 msec in Embodiment 1, welding time calculated as TP1 + TP2 + TP3 = 0.5 msec + 10 msec + 0.2 msec = 10.7 msec Although it becomes longer than 7 msec, the production time is sufficiently shorter than V = 100 mm / s when the laser scanning speed is slow as a whole and 21.4 msec when the welding appearance length L = 2.14 mm.

In Embodiment 2, during Delta] t ₄ (i.e., during the third period TP3) to the laser output, a slight proportion of the laser output P1 to the laser output P6, the scanning speed V scanning speed of the laser from the scanning speed V ₁ The amount of hot water flow can be increased due to heat conduction to the surroundings by reducing the scanning speed to ₄ and reducing the scanning speed. As a result, the amount of molten pool (the amount of hot water flow) in the down slope portion DS can be further increased than in the first embodiment.

  Thus, in Embodiment 1 and Embodiment 2, it is possible to suppress the occurrence of perforation at the time of laser welding of the battery case bottom portion 13 and to prevent leakage of the electrolyte. Electrolyte leakage makes it difficult to use the electronic device for a long period of time due to deterioration of battery performance or corrosion of surrounding metal parts. Electrolyte is also harmful to the human body. In addition, leakage in the process during battery production is likely to cause corrosion of equipment in the process or corrosion of other batteries. Therefore, measures should be taken so that the perforation of the battery case bottom 13 does not flow to the subsequent process. Must.

  In addition, it can be made to show the effect which each has by combining arbitrary embodiment or modification of the said various embodiment or modification suitably. In addition, combinations of the embodiments, combinations of the examples, or combinations of the embodiments and examples are possible, and combinations of features in different embodiments or examples are also possible.

  According to the welded structure and the manufacturing method thereof of the present disclosure, it is possible to suppress the generation of keyholes, and it can be applied to highly robust laser welding applications such as batteries or electronic components.

DESCRIPTION OF SYMBOLS 1 Positive electrode plate 2 Negative electrode plate 3 Separator 4 Electrode group 5 Battery case 6 Gasket 7 Pulse laser 10 Sealing plate 11 Positive electrode tab 12 Contact rod 13 Battery case bottom part 14 Negative electrode tab 15 Welding part 15A Welding part 15B Laser irradiation part of a welding part End 16 Continuous-wave laser 17 Resin-based foreign material 18 Welded part surface 19 Keyhole 20 Past keyhole 21 Hot water flow 22 Molten pool 23 Solidified part 24 Rise of molten pool 25 Upper pressure 26 Blow hole 27 Expanded keyhole 28 Through hole 31 Joining Unit 32 Integral value of laser output at minimum resolution of output control (0.1 ms) 33 Line connecting average values of laser output at each time 34 Inflection point 35 of down slope portion It can be made into a down slope portion due to dispersion of laser output New junction DS between the battery case bottom 13 and the negative electrode tab 14 Rope part DS1 1st down slope part DS2 2nd down slope part TP1 1st period TP2 2nd period TP3 3rd period

Claims (6)

A method of manufacturing a welded structure welded by scanning a laser from the outer surface of the battery case in a state where the inner surface of the battery case is in close contact with the electrode tab,
Forming a linear welding mark by relative movement between the laser and the battery case;
In the process,
During the first period after the start of the laser irradiation, the laser output is increased to the first output, the battery case is melted until the electrode tab is melted at the first output, and then
During the second period, maintaining the first output, melting the electrode tab and the battery case, then
Decreasing the output of the laser from the first output to a second output that melts only the battery case, then
When the second output is maintained until the end of the formation of the weld mark, or the amount of decrease in the laser output from the second output is reduced from the first output to the second output The manufacturing method of a welded structure which makes it smaller than the reduction | decrease amount.   2. The method for manufacturing a welded structure according to claim 1, wherein the first output is 800 W to 850 W, the second output is 770 to 820 W, and the first output is larger than the second output. . A welding portion for joining the battery case and the electrode tab so that the inner surface of the battery case is in close contact with the electrode tab;
The weld is continuously formed from the outer surface of the battery case to the inside of the electrode tab,
In the cross-section in the thickness direction of the electrode tab, the weld portion includes a first down slope portion and a second down slope portion positioned on an outer side of the first down slope portion in a side region of the weld portion. Have
The first down slope portion exists across both regions of the electrode tab and the battery case and its thickness gradually decreases toward the outside.
The second down slope portion is present only in a region in the battery case, and the thickness change amount is smaller than that of the first down slope portion.   4. The welded structure according to claim 3, wherein a thickness of the second down slope portion is not less than 50% and not more than 97% of a thickness of the battery case.   The welded structure according to claim 3 or 4, wherein a thickness of the second down slope portion is constant.   The width of the welded part appearance corresponding to the second down slope part of the welded part on the outer surface of the battery case is larger than the width of the central part of the welded part. The welded structure according to one.